Prashant,
NAPI performance gain is only when then packets are small in size. Without
NAPI, the number of interrupts per packet is high with small packets. This
is mitigated by the polling functionality of NAPI, which handles the
packets without (err...relatively few) have to take interrupts.
It is better explained at
"http://lxr.linux.no/source/Documentation/networking/NAPI_HOWTO.txt?v=2.6.5";
With regard to better performance when using smaller ring sizes, this can
be attributed to a knock-on effect of cache aligning the buffers. This
occurs on all adapters, and the optimal descriptor ring size differs
depending on your hardware.
Thanks,
Jon Mason jonmason@xxxxxxxxxx
Software Engineer Phone:(512)838.4162
Linux eServer I/O Fax: (512)838.3509
prashant s <sree_prash@xxxxxxxxx>
Sent by: netdev-bounce@xxxxxxxxxxx
04/24/04 03:33 PM
To: netdev@xxxxxxxxxxx
cc:
Subject: help on NAPI
sir,
i have a doubt regarding the NAPI feature which is
introduced in 2.6.3 linux.
i did not find any performance difference between the
NAPI driver (rtl 8139too 2.6.3 linux) and non NAPI
driver(rtl 8139too 2.4.20 linux) both of them showed
94Mbps(packet size of 1500bytes). The network card
which i used was a 100Mbps real tek card, and the
machine was a p 4. but when i reduced the DMA receive
ring size from 32K to 8k the NAPI driver showed 94Mbps
where as the non NAPI driver showed 72Mbps.
why is this performance difference when the ring size
is reduced.
waiting for your reply.
prashant
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